document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=971639>Question 971639</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A book publisher estimates that the total number of sales of a<BR>\n" );
document.write( "particular book, after the first 15 weeks, can be modelled by the linear<BR>\n" );
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document.write( "s = 1400(t &#8722; 15) + 150 000 (t &#8805; 15),\r<BR>\n" );
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document.write( "where s is the total number of sales, and t is the time on sale in weeks\r<BR>\n" );
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document.write( "(i) Find the number of sales after 24 weeks\r<BR>\n" );
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document.write( "(ii) Calculate the week at which the total number of sales reaches<BR>\n" );
document.write( "171 000\r<BR>\n" );
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document.write( "(iii) Write down the gradient of the straight line represented by the<BR>\n" );
document.write( "equation<BR>\n" );
document.write( "s = 1400(t &#8722; 15) + 150 000\r<BR>\n" );
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document.write( "What does this measure in the practical situation being modelled?\r<BR>\n" );
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document.write( "(iv) Explain why the vertical s-intercept of a graph of s is not 150 000\r<BR>\n" );
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document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #594052 by </B><A HREF=/tutors/aboutme.mpl?userid=amarjeeth123><B>amarjeeth123(569)</B></A><img src=\"/images/stars/stars-10.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=amarjeeth123><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=594052\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> s = 1400(t &#8722; 15) + 150 000 (t &#8805; 15)<BR>\n" );
document.write( "Plugging in the values we get,<BR>\n" );
document.write( "(i)Number of sales after 24 weeks s=1400(24-15)+150000=1400(9)+150000=12600+150000=162600<BR>\n" );
document.write( "(ii)171000=1400(t &#8722; 15)+150000<BR>\n" );
document.write( "    1400(t-15)=21000<BR>\n" );
document.write( "    t-15=15<BR>\n" );
document.write( "    t=30<BR>\n" );
document.write( "(iii)s=1400(t&#8722;15)+150000<BR>\n" );
document.write( "     s=1400t+129000<BR>\n" );
document.write( "     Comparing this with y=mx+c we get,<BR>\n" );
document.write( "     The gradient of the straight line is 1400.<BR>\n" );
document.write( "     This measures the incremental rate of publishing the book per week.<BR>\n" );
document.write( "(iv)The vertical intercept of the graph is 129000.  </SPAN>\n" );
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